Hydrogen is very important feedstock for many chemical and petrochemical processes. It is commonly produced using Steam Methane Reforming, Partial Oxidation, Auto thermal Reforming, and Gasification etc. Carbonaceous feedstock like natural gas, coal, biomass etc. along with oxidizing agent like steam or oxygen undergoes reforming reaction to produce synthesis gas (syngas). Syngas is a mixture of hydrogen, carbon monoxide, carbon dioxide, water and un-reacted methane. Reforming reaction is highly endothermic occurring at very high temperatures of 800-1300 C and high pressures of 20-80 bar. The reforming reaction can be catalytic or non-catalytic process. Excess steam is produced in the process of cooling down syngas and flue gas. The heat required for the highly endothermic reforming reaction is provided by combustion of the carbonaceous feedstock and carbon containing off-gas. The combustion process is associated with generating greenhouse gas, carbon dioxide (CO2) emissions. Syngas from reformer is further sent to water gas shift reactor to produce additional hydrogen from carbon monoxide. Water gas shift reaction produce additional carbon dioxide during the reaction. Syngas rich in hydrogen from water gas shift is further purified in a Pressure Swing Adsorption (PSA) process to produce pure hydrogen and PSA off-gas which is further used as fuel. Hydrogen production is associated with large amounts of carbon dioxide emissions. With current advancement in greenhouse gas regulations, research is underway to capture carbon dioxide from conventional hydrogen plants or reduce emissions from hydrogen plants.
Methane can be converted to hydrogen using conventional hydrogen production methods at equilibrium conditions. However, very high temperatures >900° C. and low pressures <30 bar are needed in order to achieve high methane conversions >85%. In order to provide high temperatures required for the reaction the amount of fuel consumed is very high emitting large amounts of carbon dioxide. The use of membrane reactor includes reaction and separation in the same unit allowing methane conversion higher than equilibrium conversion rate at much lower temperatures.
Membrane reactors have been used beneficially to produce hydrogen with higher methane conversion at low temperatures and simultaneously produce carbon dioxide rich stream on the retentate side with ease of CO2 capture. Membranes addition inside the reactor enables the reforming and water gas shift reaction to proceed at rates higher than equilibrium. However, one of the main disadvantages of using membrane reactors is hydrogen production at low pressure <3 bar. The cost associated with compressing hydrogen product is very high and increases the overall cost of membrane reactor.